THE ORDERS OF TRUE TUMOURS 285 



possible. To attempt to indicate the class to which each in- 

 dividual tumour belongs would immediately involve us in a 

 long and, for present purposes, absolutely fruitless discussion. 

 And this, it would seem, very largely because a tumour of one 

 histological type may be produced under different conditions. 

 Carcinoma, for example, may develop in connexion with the 

 functionless or relatively functionless cells of the ovarian dermoid ; 

 or, again, may originate from the active and functional cells of, 

 say, the gall-bladder or the splenic flexure of the colon. 



The following classification appears to me to include every 

 form even if this be the case, and even if at the present time 

 we may differ as to the class in which certain varieties of tumours 

 should be placed. 



A. TERATOMATA 



Tumours composed of the products of growth of one individual 

 within the tissues of another individual of the same species. 



I. Teratomata of the first order Twin Teratomata. Tumours 

 due to the continued growth, within the tissues of one individual, 

 of the tissues and organs of another individual which has become 

 included in the former during foetal life. 



II. Teratomata of the second order Filial Teratomata. 

 Tumours due to the continued growth, within the tissues of one 

 individual, of tissues and organs which are the product of growth 

 of one of the germ cells of that individual. 



(i.) Parthenogenetic. Tumours formed of the products of 

 the unfertilized germ cell. The more recent studies 

 of Repin 1 and Arnsperger 2 most strongly support the 

 view that ovarian and testicular dermoids can only 

 be regarded as examples of abortive parthenogenesis. 



(ii.) Gamogenetic. Tumours formed of the products of the 

 fertilized germ cell. The recent work of H. Peters 3 

 has settled the angry discussion as to the nature of 



1 Repin, " Origine parthenogenetique des kystes dennoldes de 1'ovaire," 

 These de Paris, 1892. 



1 Arnsperger, Virch. Arch. Bd. clvi., 1899, S. 1 ; see also Wilms, Deut. 

 Arch. /. Idin. Med. lv., 1895, S. 219 ; Zeigler's Beitr. xix., 1896, S. 233 and 

 367. 



1 H. Peters, Die Einbettung des menschlichen Eies, Leipzig und Vienna 

 (Deuticke), 1899. 



